Minor Actinides Content Research Articles

Examination of the use of thorium-based fuel for burning minor actinides in European sodium cooled fast reactor

Abstract To reduce the potential and volume of radiotoxicity of radioactive wastes, minor actinides (MAs) elements recovered from discharged fuel are to be recycled. In this context, the main aim of this work is to examine the possibility of using thorium-based fuel for burning extra MAs in the fourth generation European Sodium cooled Fast Reactor (ESFR). For that MCNPX transport code was used to design a representative fuel assembly of this concept. The reference uranium-based fuel was uniformly replaced by thorium mixed with different fractions of MAs and burned for 2050 effective full power days. The influence of MAs on the evolution of reactivity and fuel transmutation is being investigated to ensure the performance of the fuel. Also, different neutronic and safety parameters such as neutron yield, neutron spectrum, neutron flux, effective delayed neutron fraction, Doppler constant, sodium void reactivity coefficient, were computed and their change with MAs content was investigated. Results indicate that recycling of MAs in ESFR using thorium-based fuel has a positive effect on reactivity and transmutation evolution but on other hand has a negative effect on safety parameters.

A safety enhanced sodium-cooled MOX fueled fast reactor core concept

ABSTRACT We have developed a 750MWe sodium-cooled MOX fueled fast reactor core with enhanced safety against typical ATWS. Design goals were set as follows: 1) negative void reactivity for the loss of flow (ULOF); and 2) burnup reactivity less than 1 $ for the transient over power (UTOP). To achieve the goals the following were considered: 1) adoption of the axially heterogeneous core with a sodium plenum and a gas expansion module to reduce void reactivity; and 2) addition of minor actinides (MAs) to the internal blanket to reduce burnup reactivity. Configurations of the core were optimized as follows. First, void reactivity was reduced by a parameter survey for the inner core height, B-10 content of the upper shield, and standby position of the backup control rods. Second, burnup reactivity was reduced by a parameter survey for the MA content in the internal blanket, etc. We designed the safety enhanced fast reactor core that did not undergo sodium boiling if the ULOF occurred and we maintained fuel integrity for the UTOP by the transient analysis. By installing a self-actuated shutdown system in the backup control rods, the improved operational reliability of this shutdown system and the improved safety can be expected.

Inert-matrix fuel for transmutation: Selected mid- and long-term effects on reprocessing, fuel fabrication and inventory sent to final disposal

Partitioning and transmutation (P&T) fuel cycles provide a technical approach to ease the problem of radioactive waste disposal. Some of the partitioned components of the waste stream are irradiated while others can be used for energy production or are sent to final storage. Minor actinides are planned to be irradiated in a fast spectrum nuclear facility to transmute them into stable or short-lived isotopes. As minor actinides have negative effects on reactor dynamics, subcritical, accelerator-driven systems are proposed to increase their fraction in the fuel. An example is the MYRRHA research reactor to be built in Mol, Belgium.This reactor is modeled for depletion calculations. The behavior of special fuel elements that mirror fuel composition as envisioned for large scale transmutation facilities, namely inert-matrix fuels with an increased minor actinide content, are investigated within this reactor environment. It turns out that gamma dose rates, activity and residual heat from the spent fuel elements present significant challenges for implementing a P&T program. Spent inert-matrix fuel element show significantly higher levels than spent fuel elements from fast reactors. This requires long cooling periods and poses unprecedented challenges to reprocessing technology. The problem is amplified by the fact that it is generally agreed upon that due to low transmutation efficiencies several transmutation steps would be necessary. Looking at the radiotoxicity index, the efforts suggested to reduce the minor actinide content in a final repository are justified. The long-term safety case of deep geological repositories, however, implies that certain long-lived fission products are more relevant. The build-up of some of these radionuclides is investigated for two hypothetical German P&T scenarios. Naturally, the amount of fission products increases with continued irradiation. But namely the fraction of Cs-135 increases over-proportionally when inert-matrix fuel rich on minor actinides is used.

Modelling of thermal conductivity and melting behaviour of minor actinide-MOX fuels and assessment against experimental and molecular dynamics data

• Modelling of thermal conductivity and melting temperature of minor actinide-MOX fuels. • Review of state-of-the-art data and correlations available in literature or in codes. • Inclusion of the effect of the homogeneous minor actinides Am and Np. • Separate-effect assessment against literature data, experimental and MD-calculated. • Integral application to the performance of a fast reactor, MA-MOX fuel pin. Recycling and burning minor actinides (MA, e.g., americium, neptunium) in mixed-oxide (MOX) nuclear fuel is a strategic option for fast reactor concepts of Generation IV, especially considering the current interest in the ultimate radioactive waste management and sustainability improvement by better use of natural resources. Among the fuel properties, thermal conductivity and melting temperature are pivotal since they determine, respectively, the fuel temperature profile and the fundamental safety limit on the margin to fuel melting, hence impacting on the overall fuel performance under irradiation and allowing the safe irradiation of the fuel pin. Nevertheless, the available literature about Am- or Np-containing MOX is currently scarce, both regarding experimental data and models. Moreover, state-of-the-art fuel performance codes (FPCs, e.g., TRANSURANUS) do not account for the effects of minor actinides on MOX fuel properties. This work presents original correlations for thermal conductivity and melting temperature of minor actinide-MOX fuels, i.e., (U, Pu, Am, Np)O 2-x , derived based on the available literature and accessible data, which are herein extensively reviewed. The assessment of the novel correlations is first performed in a statistical way, evaluating the regressor p-values which indicate their significance with respect to the available experimental dataset used for the fitting procedure. Additionally, the novel correlations for MA-MOX are assessed against both measured and calculated data (from Molecular Dynamics simulations), yielding an accuracy in line with the already existing correlations and with the state-of-the-art experimental uncertainties. Finally, the potential integral impact of a homogeneous minor actinide content in the fuel is illustrated on the basis of a fuel pin fast-ramped up to fuel melting during the HEDL P-19 irradiation experiment.

SUPERFACT: A Model Fuel for Studying the Evolution of the Microstructure of Spent Nuclear Fuel during Storage/Disposal.

The transmutation of minor actinides (in particular, Np and Am), which are among the main contributors to spent fuel α-radiotoxicity, was studied in the SUPERFACT irradiation. Several types of transmutation UO2-based fuels were produced, differing by their minor actinide content (241Am, 237Np, Pu), and irradiated in the Phénix fast reactor. Due to the high content in rather short-lived alpha-decaying actinides, both the archive, but also the irradiated fuels, cumulated an alpha dose during a laboratory time scale, which is comparable to that of standard LWR fuels during centuries/millenaries of storage. Transmission Electron Microscopy was performed to assess the evolution of the microstructure of the SUPERFACT archive and irradiated fuel. This was compared to conventional irradiated spent fuel (i.e., after years of storage) and to other 238Pu-doped UO2 for which the equivalent storage time would span over centuries. It could be shown that the microstructure of these fluorites does not degrade significantly from low to very high alpha-damage doses, and that helium bubbles precipitate.

Physical studies of minor actinide transmutation in the accelerator-driven subcritical system

The accelerator-driven subcritical system (ADS) with a hard neutron energy spectrum was used to study transmutation of minor actinides (MAs). The aim of the study was to improve the efficiency of MA transmutation while ensuring that variations in the effective multiplication factor (keff) remained within safe margins during reactor operation. All calculations were completed using code COUPLE3.0. The subcritical reactor was operated at a thermal power level of 800 MW, and a mixture of mono-nitrides of MAs and plutonium (Pu) was used as fuel. Zirconium nitride (ZrN) was used as an inert matrix in the fuel elements. The initial mass composition in terms of weight percentages in the heavy metal component (IHM) was 30.6% Pu/IHM and 69.4% MA/IHM. To verify the feasibility of this MA loading scheme, variations in keff, the amplification factor of the core, maximum power density and the content of MAs and Pu were calculated over six refueling cycles. Each cycle was of 600 days duration, and therefore, there were 3600 effective full power days. Results demonstrated that the effective transmutation support ratio of MAs was approximately 28, and the ADS was able to efficiently transmute MAs. The changes in other physical parameters were also within their normal ranges. It is concluded that the proposed MA transmutation scheme for an ADS core is reasonable.

Minor Actinide Transmutation in Supercritical-CO2-Cooled and Sodium-Cooled Fast Reactors with Low Burnup Reactivity Swings

This paper presents the investigation of minor actinide (MA) transmutation in supercritical CO2-cooled and sodium-cooled fast reactors (S-CO2-FR and SFR) with the thermal output of 600 MW(thermal) for simultaneously attaining low burnup reactivity swings and reducing long-life radioactive waste. Minor actinides are loaded uniformly in the fuel of the cores, and the MA contents are determined to minimize the burnup reactivity swings. In the S-CO2-FR, the burnup reactivity swing is minimized to 0.11% ∆k/kk’ when the MA content is 6.0 wt%. In the SFR, the MA content was determined to reduce the burnup reactivity swing while maintaining sodium void reactivity under a design limitation of 5 $. The burnup reactivity swing of the SFR is reduced to 1.94% ∆k/kk’, whereas sodium void reactivity is about 4.7 $ when 10.0 wt% MAs are loaded. The low burnup reactivity swing enables minimization of control rod operation during fuel burnup. The number of control rods in the two reactors is reduced to ten, which is half of a typical sodium-cooled mixed-oxide fuel MONJU reactor without MA loading. The MA transmutation rates in the S-CO2-FR and SFR are 42.2 and 52.2 kg/year, respectively, which are equivalent to the production rates in seven and nine light water reactors of the same electrical output.

Lead reactor of small power with metallic fuel

The possibility for obtaining a hard neutron spectrum in small reactor cores has been considered. A harder spectrum than spectra in known fast sodium cooled and molten salt reactors has been obtained thanks to the selection of relatively small core dimensions and the use of metallic fuel and natural lead (natPb) coolant. The calculations for these compositions achieve an increased average neutron energy and a large fraction of hard neutrons in the spectrum (with energies greater than 0.8 MeV) caused by a minor inelastic interaction of neutrons with the fuel with no light chemical elements and with the coolant containing 52.3% of 208Pb, a low neutron-moderating isotope. An interest in creating reactors with a hard neutron spectrum is explained by the fact that such reactors can be practically used as special burners of minor actinides (MA), and as isotope production and research reactors with new consumer properties. With uranium oxide fuel (UO2) substituted by metallic uranium-plutonium fuel (U-Pu-Zr), the reactors under consideration have the average energy of neutrons and the fraction of hard neutrons increasing from 0.554 to 0.724 MeV and from 18 to 28% respectively. At the same time, the one-group fission cross-section of 241Am increases from 0.359 to 0.536 barn, while the probability of the 241Am fission increases from 22 to 39%. It is proposed that power-grade plutonium resulting from regeneration of irradiated fuel from fast sodium cooled power reactors be used as part of the fuel for future burner reactors. It contains unburnt plutonium isotopes and some 1% of MAs which transmutate into fission products in the process of being reburnt in a harder spectrum. This will make it possible to reduce the MA content in the burner reactor spent fuel and to facilitate so the long-term storage conditions for high-level nuclear waste in dedicated devices.

Characteristics of a gas-cooled fast reactor with minor actinide loading

This paper presents the neutronics characteristics of a prototype gas-cooled (supercritical CO2-cooled) fast reactor (GCFR) with minor actinide (MA) loading in the fuel. The GCFR core is designed with a thermal output of 600 MWt as a part of a direct supercritical CO2 (S-CO2) gas turbine cycle. Transmutation of MAs in the GCFR has been investigated for attaining low burnup reactivity swing and reducing long-life radioactive waste. Minor actinides are loaded uniformly in the fuel regions of the core. The burnup reactivity swing is minimized to 0.11% ∆k/kk’ over the cycle length of 10 years when the MA content is 6.0 wt%. The low burnup reactivity swing enables minimization of control rod operation during burnup. The MA transmutation rate is 42.2 kg/yr, which is equivalent to the production rates in 7 LWRs of the same electrical output.

On the influence of the americium isotopic vector on the cooling time of minor actinides bearing blankets in fast reactors

In the heterogeneous minor actinides transmutation approach, the nuclei to be transmuted are loaded in dedicated targets often located at the core periphery, so that long-lived heavy nuclides are turned into shorter-lived fission products by fission. To compensate for low flux level at the core periphery, the minor actinides content in the targets is set relatively high (around 20 at.%), which has a negative impact on the reprocessing of the targets due to their important decay heat level. After a complete analysis of the main contributors to the heat load of the irradiated targets, it is shown here that the choice of the reprocessing order of the various feeds of americium from the fuel cycle depends on the actual limit for fuel reprocessing. If reprocessing of hot targets is possible, it is more interesting to reprocess first the americium feed with a high243Am content in order to limit the total cooling time of the targets, while if reprocessing of targets is limited by their decay heat, it is more interesting to wait for an increase in the241Am content before loading the americium in the core. An optimization of the reprocessing order appears to lead to a decrease of the total cooling time by 15 years compared to a situation where all the americium feeds are mixed together when two feeds from SFR are considered with a high reprocessing limit.

Uncertainty analysis of minor actinides transmutation in fast reactor cores

The uncertainty of minor actinides transmutation in fast reactors has been estimated for individual nuclides of minor actinides (MA). The burn-up dependent sensitivities of MA number densities are calculated using the generalized perturbation theory, and a method is derived to transform the sensitivities to the sensitivities of minor actinides transmutation. The sensitivities are used to obtain the uncertainties of minor actinides transmutation together with the cross-section covariance data of JENDL-4. The method is applied to the two MA transmutation fast reactor cores with MA content of 6% and 11%. It is seen that the uncertainties of the total MA transmutation amounts are about 3% and 4% for the two cores because the uncertainties of Np-237 and Am-241 transmutations which mainly contribute the total transmutation are small (about 3%).The contribution to the uncertainties is mainly caused by the Np-237 and Am-241 capture cross-sections.The transmutation uncertainties for Np-239, Am-233, Cm-243, and Cm-245 are rather large. However the transmutation amounts of these nuclides are very small, and the large uncertainties are not the problem in practice. However, it is found that the transmutation amount of Cm-244 has large uncertainties of 10% and 13% for the cores with MA content of 6% and 11%, and this large uncertainties have to be considered when MA fuels are fabricated and reprocessed because Cm-244 produces large decay heat and neutron emission.

COSI6: A Tool for Nuclear Transition Scenario Studies and Application to SFR Deployment Scenarios with Minor Actinide Transmutation

Nuclear systems, composed of reactors with varied fuel and cycle facilities (enrichment plant, fabrication plant, reprocessing plant, etc.), are complex and in constant evolution. Since 1985, the CEA has been developing the simulation software COSI to study different trajectories of nuclear fleet evolution and provide technical elements to decision makers. The principle of COSI, including the typical composition of the data set, is exposed. To evaluate as accurately as possible the isotopic compositions of materials, several physical models are implemented in COSI. The main ones, the evolution calculation and the equivalence models, are described in detail. An exercise of validation of COSI carried out on the French pressurized water reactor (PWR) historical nuclear fleet until 2010 is also presented, as well as a methodology for propagation of input uncertainties on COSI results.To illustrate the possibilities of COSI, the results of different scenarios studied in the framework of the French Act for Waste Management are discussed. The objective of these scenarios is to evaluate the feasibility of sodium-cooled fast reactor (SFR) deployment to renew the French PWR fleet on different timescales and to analyze the costs and the benefits of different options of minor actinide (MA) partitioning and transmutation. The impacts of SFR deployment on cycle facilities such as the fabrication plant, the spent fuel storage, and the reprocessing plant are minimized. The SFR deployment appears to be feasible with regard to fissile material availability, with an adaptation of fuel cooling time before reprocessing or of SFR breeding gain.Minor actinide transmutation in homogeneous mode MA diluted in core) and transmutation in heterogeneous mode (in MA-bearing blankets) are compared not only according to their impacts on cycle facilities and on ultimate waste but also according to the reduction of their inventories. The increases in fresh fuel thermal power and spent fuel decay heat due to the addition of MAs in fuels are quantified. The cases of transmutation of all MAs (americium, neptunium, and curium) and of americium only are distinguished. Alternative scenarios are explored to overcome the challenges associated with each option: reduction of the maximal MA content in fresh SFR fuel in the case of homogeneous transmutation and reduction of interim MA storage in the case of heterogeneous transmutation.

Study of minor actinides effect on kinetic parameters and reactivity coefficients in an accelerator driven system

The effect of minor actinides (MA) on kinetic parameters and reactivity coefficients in an accelerator driven system (ADS) is analyzed in this paper. The Italian XADS reactor with (U,Pu,MA)O2 fuel is considered as the case study of the problem, which consists of a subcritical liquid metal reactor and a proton accelerator. A new Monte Carlo method is applied to calculate the kinetic parameters, i.e., effective delayed neutron fraction (βeff), mean neutron generation time (Λ). Furthermore, Doppler coefficient (αD) and coolant feedback coefficient (αC) are obtained by calculating effective multiplication factors (keff) at various temperatures. To verify the adopted method, calculations are performed on several benchmarks. The calculated values of the new method are compared with those obtained from prompt method, 1/v absorber method and reference data. The results show that the new method could accurately calculate kinetic parameters for both critical reactors and subcritical reactors with an external source. The different percentage of MA in the fuel is studied to determine its effect on kinetic parameters and reactivity coefficients for XADS. When the content of MA reaches 5% in the fuel, the values of βeff and Λ decrease by about 18% and 31%, respectively. With the increase of MA content from 0 to 5%, the value of α¯D varies from −0.56 pcm/K to −0.36 pcm/K, and the value of α¯C varies from −2.11 pcm/K to −1.73 pcm/K.

Comparative Studies on Plutonium and Minor Actinides Utilization in Small Molten Salt Reactors with Various Powers and Core Sizes

Abstract Molten salt reactor (MSR) has many advantages such as safety improvement and ability for waste burning. In the present study, the use of plutonium and minor actinides (MA) in small MSRs with various powers and core sizes has been investigated. For the small MSRs with 50 MWth, 100 MWth, 150 MWth, 200 MWth, and 250 MWth of power output, the criticality condition can be achieved if the reactor grade plutonium and MA content in loaded fuel are 7.56%, 6.76%, 6.56%, 6.56%, and 6.56%, respectively. The plutonium and MA utilization in small MSR results in the hardening of neutron spectrum compared to that of the standard 25 MWth miniFUJI MSR with Th- 233 U fuel. Furthermore, the neutron spectra become harder with the augmenting of Pu and MA contents in loaded fuel as well as the increasing of the output power.

Minor actinides impact on basic safety parameters of medium-sized sodium-cooled fast reactor

Abstract An analysis of the influence of addition of minor actinides (MA) to the fast reactor fuel on the most important safety characteristics was performed. A special emphasis was given to the total control rods worth in order to describe qualitatively and quantitatively its change with MA content. All computations were performed with a homogeneous assembly model of modified BN-600 sodium-cooled fast reactor core with 0, 3 and 6% of MA. A model was prepared for the Monte Carlo neutron transport code MCNP5 for fresh fuel in the beginning-of-life (BOL) state. Additionally, some other parameters, such as Doppler constant, sodium void reactivity, delayed neutron fraction, neutron fluxes and neutron spectra distribution, were computed and their change with MA content was investigated. Study indicates that the total control rods worth (CRW) decreases with increasing MA inventory in the fuel and confirms that the addition of MA has a negative effect on the delayed neutron fraction.

Seed and blanket ADS using thorium–reprocessed fuel: Parametric survey on TRU transmutation performance and safety characteristics

Conceptual designs of accelerator driven systems (ADS) that utilize thorium fuel as blanket and reprocessed fuel as seed for fission reaction in order to transmute the transuranic elements in spent nuclear fuel and produce energy from thorium utilization was proposed. In order to analyze the TRU transmutation performance of the system while the safety margin during the operation is satisfied, a parametric survey is done in this study. The impact of minor actinide (MA) amount and the reactor size on transmutation efficiency and safety characteristics of the ADS is investigated using MCNPX code using the ENDF/B-VII. As the results, with increasing MA content, TRU transmutation rate is increased while void reactivity of the system becomes less negative. Besides, increasing the core size by introducing more thorium and reprocessed fuel assemblies into the system reduces the TRU transmutation rate and reactivity swing due to burnup of the system. In order to match the efficient transmutation purpose and safety features during operation, higher MA content is suggested to introduce into the system.

Accommodation of multivalent cations in fluorite-type solid solutions: Case of Am-bearing UO2

The radiotoxicity of spent nuclear fuel is mainly due to the content of minor actinides, which could be substantially reduced by Partitioning and Transmutation. A possible transmutation method would be to employ americium-bearing uranium oxide materials as blanket fuels in fast neutron reactors. In order to maintain fuel performance and reactor safety, it is mandatory to control the structural homogeneity and oxygen stoichiometry during the sintering process. In this work, U0.85Am0.15O2−x materials, fabricated by a solid state chemistry process, were sintered at 2023K under three oxygen potentials, i.e. −375, −350 and −325kJmol−1, thereby significantly extending the range of a previous study. By coupling X-ray diffraction and X-ray absorption spectroscopy measurements, it was shown that fluorite solid solutions are obtained whatever the sintering conditions. The presence of U(+V), pointed out in a previous work for oxygen potentials equal to −520 and −450kJmol−1, was confirmed. This result constitutes an experimental proof of the existence of U(+V) in An-doped UO2 fluorite-type structure materials. These experimental data are major results in view of the developing thermodynamical model of the U–Am–O system. Considering the now available extended range, the effect of the oxygen potential is discussed in terms of charge distribution and local structure.

Minor Actinide Transmutation in GFR600

Within the Generation IV initiative, the gas-cooled fast reactor (GFR) is one of the reactors dedicated to minor actinide (MA) transmutation. This paper summarizes the research performed with the GFR600 reference design in order to assess its MA burning capabilities. For the study, modules of the SCALE program system were used.Single-cycle parametric studies were performed with cores having different MA content and spatial distribution. It was shown that the addition of MAs to the fuel greatly reduced the reactivity loss during burnup. Moreover, the higher the MA content of the core, the higher the fraction of it that was fissioned; however, the more the delayed neutron fraction and the fuel temperature coefficient degraded. Significant reduction can be achieved in the amounts of neptunium and americium, while curium isotopes accumulate.The study of multiple consecutive cycles showed that by adding only depleted uranium (DU) to the reprocessed actinides in fuel fabrication (pure DU feed strategy), up to 70% of the initially loaded MAs can be fissioned in the first five cycles. Moreover, the reactor can be made critical during that time if the initial MA content is higher than 3%. By feeding MAs as well (constant MA content strategy), the reactivity has a steady increase from cycle to cycle, predominantly due to 238Pu breeding from 237Np.The effects of the isotopic composition of the plutonium and MAs were also examined by performing calculations with data specific to the spent fuel of traditional western pressure water reactors and Russian type VVER440 reactors. Despite the considerably different MA vectors, no significant deviation was found in their overall transmutation. However, the Pu composition had a strong effect on the reactivity and the delayed neutron fraction in the first cycles.Finally, cores having nonuniform MA content were investigated. It was found that though the MA destruction efficiency was significantly higher in the middle of the core than at the edge, moving some of the MAs from the outer regions to the center resulted in only minor improvement in their destruction. However, the spectral changes caused by the rearrangement increased the k-effective, which allowed higher burnups and increased MA destruction. Unfortunately, some of the safety parameters of the reactor degraded.

Near-complete transuranic waste incineration in a thorium fuelled pressurised water reactor

The production of long-lived transuranic (TRU) waste is a major disadvantage of fission-based nuclear power. Incineration, and virtual elimination, of waste stockpiles is possible in a thorium (Th) fuelled critical or subcritical fast reactor. Fuel cycles producing a net decrease in TRUs are possible in conventional pressurised water reactors (PWRs). However, minor actinides (MAs) have a detrimental effect on reactivity and stability, ultimately limiting the quality and quantity of waste that can be incinerated. In this paper, we propose using a thorium-retained-actinides fuel cycle in PWRs, where the reactor is fuelled with a mixture of thorium and TRU waste, and after discharge all actinides are reprocessed and returned to the reactor. To investigate the feasibility and performance of this fuel cycle an assembly-level analysis for a one-batch reloading strategy was completed over 125 years of operation using WIMS 9. This one-batch analysis was performed for simplicity, but allowed an indicative assessment of the performance of a four-batch fuel management strategy. The build-up of 233U in the reactor allowed continued reactive and stable operation, until all significant actinide populations had reached pseudo-equilibrium in the reactor. It was therefore possible to achieve near-complete transuranic waste incineration, even for fuels with significant MA content. The average incineration rate was initially around 330 kg per GW th year and tended towards 250 kg per GW th year over several decades: a performance comparable to that achieved in a fast reactor. Using multiple batch fuel management, competitive or improved end-of-cycle burn-up appears achievable. The void coefficient (VC), moderator temperature coefficient (MTC) and Doppler coefficient remained negative. The quantity of soluble boron required for a fixed fuel cycle length was comparable to that for enriched uranium fuel, and acceptable amounts can be added without causing a positive VC or MTC. This analysis is limited by the consideration of a single fuel assembly, and it will be necessary to perform a full core coupled neutronic–thermal-hydraulic analysis to determine if the design in its current form is feasible. In particular, the potential for positive VCs if the core is highly or locally voided is a cause for concern. However, these results provide a compelling case for further work on concept feasibility and fuel management, which is in progress.

Feasibility study of minor actinide transmutation in light water reactors with various Am/Cm separation efficiencies

A study was conducted to evaluate the feasibility of minor actinide (MA) transmutation in light water reactors (LWR). The purpose of this work was to provide a guide for future investigations into MA transmutation in LWR. This work considered the effects of various Am/Cm separation efficiencies as well as homogeneous and heterogeneous MA bearing fuel assemblies. The MA content was introduced into the reactor as mixed oxide plus minor actinide (MOX + MA) fuel. Three Am/Cm separation efficiencies were independently considered: 99.9%, 99.0%, and 90.0%. In order to evaluate the feasibility of MA transmutation, the fuel performance of the various assemblies and core designs, as well as their respective safety related parameters, were calculated. The reduction of the burden of high level waste (HLW) motivated the investigation of MA transmutation. It was found that the MA bearing fuel assemblies and their subsequent core designs were able to perform within the safety limits required as well as achieving similar burnups to a UO 2 core. The Am transmutation rates were ∼40% for the homogeneous assemblies and up to 68% for the MA targets in the heterogeneous assemblies after the described burnup, however, there was a significant amount of Cm produced during burnup. This Cm production was due to the more favorable neutron capture reaction over fission for Am in the thermal spectrum. Future work should examine the benefits of Am transmutation at the expense of large Cm production rates.